In a stunning turn of events, an Austrian on trial for imprisoning his daughter for 24 years and fathering her seven children pleaded guilty Wednesday to all charges against him — including negligent homicide — after hearing his daughter's heart-wrenching testimony.

In a change of heart, Josef Fritzl calmly acknowledged his guilt on the third day of a trial that has drawn media attention from around the world for its shocking allegations.

"I declare myself guilty to the charges in the indictment," Fritzl, 73, told a panel of judges, referring at one point to what he called "my sick behavior."

Fritzl faces up to life imprisonment on the negligent homicide count, which he initially had contested along with an enslavement charge. Prosecutors also had charged him with rape, incest, forced imprisonment and coercion...